1. Field of the Invention
The disclosure relates to oil field equipment, and particularly to oil field gate valves, such as those valves meeting pressurization specifications.
2. Description of Related Art
As in most realms, the oil field market is influenced by safety concerns balanced against cost and value for products and services. To control the minimum safety requirements, regulations and specifications are promulgated in the oil field industry, so that customers can purchase equipment necessary for projects with the expectation that the equipment will meet certain standards. Known and respected specifications for oil field equipment are promulgated by the American Petroleum Institute (“API”) that requires valves to meet rigorous tests. A significant focus is on valves and similar control devices, because of the dangers of oil field wells that are controlled by valves. One specific specification is API 6A PSL-2 PR2 for product specification level and performance requirements. A valve has to pass certain tests as virtually leak proof for an extended period of time for a gaseous medium at elevated pressures (that is, generally 5,000 psi and above) and elevated temperatures (generally 250° F. and above). The challenge is to design a valve that can meet such rigorous tests in the industry that is affordable to customers and competitive to the marketplace.
Standard design engineering for such valves generally increases the overall cross-sectional diameters and thicknesses of the valve body to add mass to the valve for increased pressure requirements and performance. The valve acts as a pressure vessel and must withstand not only the pressure, but must be stiff enough to minimize the engineering strain at stress levels to maintain alignment of the valve components which must seal, connect, rotate, translate up and down, and otherwise function for their intended purpose all without leakage at critical junctures. Most valves in the market place reflect this standard practice of adding more mass to the overall size, even though a significant portion of the valve cost is directly related to simply the amount of material in the valve body. Another common practice is to increase larger cavities for larger seals, which in turn causes increased cross-sections of the valve body, which leads to the above referenced increase in material and costs. Another practice is to rely on metal-to-metal seals, because at PR2 pressures and temperatures, rubber and elastomeric seals may extrude and fail. However, as the valve ages, the surface finish of the mating surfaces deteriorates and the valves can leak, decreasing its useful life. The challenge is to include additional sealing while keeping costs to a minimum.
These challenges have been met in various ways by the industry. Generally, the remedy is to meet the engineering tests such as the API 6A PSL-2 PR2 referenced above even at an additional cost of materials, attempt to negotiate competitive prices from suppliers of the additional components, increase manufacturing efficiency, contract offshore to other suppliers, and demand an incremental price increase.
Therefore, there remains a need to provide an improved valve that can meet such specifications and tests that are still competitive in the marketplace.